Strike and Dip

Dip is the measure of how much the bedding planes are inclined from horizontal. Using the clinometer, it is placed along the bedding plane and the angle the beds make with respect to horizontal is measured. In the example at the left, the dip angle is 32 degrees. Next we measure the direction that the dip angle was measured. Dip is always measured perpendicular to strike. It is important to notate the direction of dip since there are two possible outcomes, not notating the direction of dip could lead a geologist to draw inaccurate conclusions about the rocks being measured. In our example at the left, the direction of dip is south 10 degrees west (S10W) or 190 degrees. On a geologic map, the dip is a tick mark perpendicular to the strike line facing in the direction of dip with the angle of the dip written next to the symbol. When measuring strike and dip, always try to place a notebook or other smooth surface along the bedding surface to be measured so any irregularities in the surface are evened out.

There are several methods that can be used for measuring strike and dip. The method outlined above is usable for most small outcrops and surfaces. On very large outcrops, the geologist must move away from the outcrop and select a bedding surface with an attitude representing the entire outcrop. The geologist then moves so the bedding surface appears as a two-dimensional line. This is the projected plane of the bedding surface. The geologist then uses a clinometer as a hand level, creating a horizontal line with respect to the bedding surface and thus allowing the geologist to measure the strike. From the same position, the dip is measured by sighting the clinometer at arms length along the bedding plane.

Sometimes it is necessary to measure strike and dip using a three-point method. This method is useful when the geologist has access to a geologic map, or must be done when the geologist does not have a compass and clinometer. This method is also useful for measuring very gently sloping surfaces or for surfaces that dip over large areas. This method requires the geologist to determine the horizontal position and elevations of three separate points on the bedding plane. The points need to define a triangle with internal angels greater than 20 degrees. When using a map, the sides of the

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